高墩大跨连续刚构桥抗震影响因素研究
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摘要
高墩大跨连续刚构桥是一种被广泛应用的桥梁结构形式,其地震响应与常见的中小跨径桥梁的地震响应有所不同。桥墩的截面形式、桥墩高差、墩梁的刚度比等设计参数的取值、桩土效应、行波效应、结构非线性等都会对此类桥梁的抗震性能产生不同程度的影响。对高墩大跨连续刚构桥抗震相关影响因素进行研究,对于提高这类桥梁的设计质量、确保桥梁结构的安全,具有重要的理论和现实意义。本文借助于大型有限元软件MIDAS/Civil,侧重研究了桥墩参数、桩土效应对高墩大跨连续刚构桥抗震性能的影响效应,主要得出以下五项结论：
1.双肢薄壁墩截面形式对高墩大跨连续刚构桥的高阶振型影响较大,对竖向振型质量参与系数影响较大,空心墩抗震性能要优于实心墩。
2.双肢薄壁墩间距在L/12～L/30范围时,高墩大跨连续刚构桥动力力特性基本相同,地震力作用下墩底弯矩、剪力随着间距的增大,呈线性递增。双肢薄壁墩双肢间距在常规的L/20～L/25范围变化时,整个桥梁在地震作用下的墩底弯矩、墩底剪力变化在5.5%以内、位移的变化在2%以内。
3.当高墩大跨连续刚构桥存在高低墩时,随着桥墩相对高差的增大,三个方向的整体刚度都有一定的增大；随着相对高差的增大,在地震作用下,高墩的墩底弯矩、剪力呈减少趋势,矮墩的墩底弯矩、剪力有增大趋势。
4.考虑桩土效应后,高墩大跨连续刚构桥动力特性发生改变,自振频率变小,结构变柔,桩土效应对横向频率影响较为显著；在弹性状态下,反应谱分析和弹性时程计算结果都显示,考虑桩土效应后,墩底弯矩减小、剪力减少,位移反应增大。
5.罕遇地震下高墩大跨连续刚构桥弹塑性时程分析表明：考虑桩土效应后,高墩大跨连续刚构桥墩底弯矩减少,剪力变化较为复杂。地震动横向输入,塑性铰先发生在墩底,固结模型的塑性铰变形大于桩土模型；纵向输入时,墩顶塑性铰先于墩底出现塑性变形,墩顶位置桩土模型大于固结模型,墩底位置桩土模型小于固结模型。
High-pier Long-span Continuous Rigid Frame Bridge is a widely used form in bridge engineering whose seismic response is quite different from the common span bridges.The anti-seismic performance of this bridge can be influenced by many factors with different degrees, such as the section form of bridge pier section, the height of bridge piers, the properties of the stiffness ratio of the bridge pier,the pile-soil effection,thaveling wave effect and the nonlinear of structure. The study of anti-seismic factors of the rigid frame bridge which can be used to improve the design quality and ensure the safety of the bridge structure is of great theoretical and practical significance. Using large finite numerical simulation software MIDAS/Civil and focusing on researching the influences to anti-seismic performance of the bidge caused by pile-soil interaction and parameters of the piers,the thesis has got the following five major conclusions:
Firstly, the section type of double-shaft thin-wall piers has great effects on both the higher modes and the vertical modes participation factors of high-pier long-span continuous rigid frame bridge. The anti-seismic of hollow piers is better than solid ones.
Secondly, when the span of double-shaft thin-wall pier is between L/12-L/30, the bridge has almost the same dynamic characteristics,while the shears and moments at the bottom of piers increase progressively with the expansions of span. However, when the span varies between L/2～0L/25, the shears and moments at the bottom of the piers change within5.5%and the displacements change within2%.
Thirdly, if both high and low piers exist in one high-pier long-span continuous rigid frame bridge, the whole stiffness enlarges in three directions as the relative elevation enlarges. But the bending moment and the shear of high pier present a decreasing trend compared to an increasing trend presented of the low pier when the relative elevation enlarges.
Fourthly, considering the pile-soil effect, the dynamic characteristics of the high-pier long-span continuous rigid frame bridge change and the natural frequency decreases which makes the whole structure softer. The pile-soil effect has even greater influences on transverse frequency. The response spectrum analysis and the calculation results of elastic time-history both show that if the bridge is under the elastic state,the moments at the bottom of the piers decrease,while the shear and the displacement actions increase.
Finally, the elastic-plastic time-history analysis of the high-pier long-span continuous rigid frame bridge in rare earthquakes present: considering the pile-soil effect, the moments at the bottom of the piers of the bridge decrease and the shear becomes more complicated. When the seismic oscillation is input laterally, the plastic hinge first appears at the bottom of the pier. And the plastic hinge's deformations of consolidation model are larger than that of the pile-solid model.When the seismic oscillation is input longitudinally, the plastic hinge's deformations at the top of piers appear earlier than that at the bottom, and pile-soil model at the top is larger than the consolidation model while pile-soil model at the bottom is less than the consolidation model.
1.双肢薄壁墩截面形式对高墩大跨连续刚构桥的高阶振型影响较大,对竖向振型质量参与系数影响较大,空心墩抗震性能要优于实心墩。
2.双肢薄壁墩间距在L/12～L/30范围时,高墩大跨连续刚构桥动力力特性基本相同,地震力作用下墩底弯矩、剪力随着间距的增大,呈线性递增。双肢薄壁墩双肢间距在常规的L/20～L/25范围变化时,整个桥梁在地震作用下的墩底弯矩、墩底剪力变化在5.5%以内、位移的变化在2%以内。
3.当高墩大跨连续刚构桥存在高低墩时,随着桥墩相对高差的增大,三个方向的整体刚度都有一定的增大；随着相对高差的增大,在地震作用下,高墩的墩底弯矩、剪力呈减少趋势,矮墩的墩底弯矩、剪力有增大趋势。
4.考虑桩土效应后,高墩大跨连续刚构桥动力特性发生改变,自振频率变小,结构变柔,桩土效应对横向频率影响较为显著；在弹性状态下,反应谱分析和弹性时程计算结果都显示,考虑桩土效应后,墩底弯矩减小、剪力减少,位移反应增大。
5.罕遇地震下高墩大跨连续刚构桥弹塑性时程分析表明：考虑桩土效应后,高墩大跨连续刚构桥墩底弯矩减少,剪力变化较为复杂。地震动横向输入,塑性铰先发生在墩底,固结模型的塑性铰变形大于桩土模型；纵向输入时,墩顶塑性铰先于墩底出现塑性变形,墩顶位置桩土模型大于固结模型,墩底位置桩土模型小于固结模型。
High-pier Long-span Continuous Rigid Frame Bridge is a widely used form in bridge engineering whose seismic response is quite different from the common span bridges.The anti-seismic performance of this bridge can be influenced by many factors with different degrees, such as the section form of bridge pier section, the height of bridge piers, the properties of the stiffness ratio of the bridge pier,the pile-soil effection,thaveling wave effect and the nonlinear of structure. The study of anti-seismic factors of the rigid frame bridge which can be used to improve the design quality and ensure the safety of the bridge structure is of great theoretical and practical significance. Using large finite numerical simulation software MIDAS/Civil and focusing on researching the influences to anti-seismic performance of the bidge caused by pile-soil interaction and parameters of the piers,the thesis has got the following five major conclusions:
Firstly, the section type of double-shaft thin-wall piers has great effects on both the higher modes and the vertical modes participation factors of high-pier long-span continuous rigid frame bridge. The anti-seismic of hollow piers is better than solid ones.
Secondly, when the span of double-shaft thin-wall pier is between L/12-L/30, the bridge has almost the same dynamic characteristics,while the shears and moments at the bottom of piers increase progressively with the expansions of span. However, when the span varies between L/2～0L/25, the shears and moments at the bottom of the piers change within5.5%and the displacements change within2%.
Thirdly, if both high and low piers exist in one high-pier long-span continuous rigid frame bridge, the whole stiffness enlarges in three directions as the relative elevation enlarges. But the bending moment and the shear of high pier present a decreasing trend compared to an increasing trend presented of the low pier when the relative elevation enlarges.
Fourthly, considering the pile-soil effect, the dynamic characteristics of the high-pier long-span continuous rigid frame bridge change and the natural frequency decreases which makes the whole structure softer. The pile-soil effect has even greater influences on transverse frequency. The response spectrum analysis and the calculation results of elastic time-history both show that if the bridge is under the elastic state,the moments at the bottom of the piers decrease,while the shear and the displacement actions increase.
Finally, the elastic-plastic time-history analysis of the high-pier long-span continuous rigid frame bridge in rare earthquakes present: considering the pile-soil effect, the moments at the bottom of the piers of the bridge decrease and the shear becomes more complicated. When the seismic oscillation is input laterally, the plastic hinge first appears at the bottom of the pier. And the plastic hinge's deformations of consolidation model are larger than that of the pile-solid model.When the seismic oscillation is input longitudinally, the plastic hinge's deformations at the top of piers appear earlier than that at the bottom, and pile-soil model at the top is larger than the consolidation model while pile-soil model at the bottom is less than the consolidation model.
引文
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[3]范立础.桥梁工程[M].北京：人民交通出版社,2004
[4]马保林.高墩大跨连续刚构桥[M].北京：人民交通出版社,2002
[5]重庆交通科研设计院.JTG/T B02-01—-2008公路桥梁抗震细则.北京：人民交通出版社,2008
[6]郑史雄等.大跨度刚构桥的地震反应分析[J].西南交通大学学报.1997,32(6)：586-592
[7]李艳明,王留洋.空心墩和实心墩对连续刚构桥受力影响的比较[J].铁道标准设计.2005,6：63-64
[8]崔海琴等.空心矩形薄壁墩延性抗震性能试验[J].公路交通技.2010,27(6)：59-63
[9]竹晓华.连续刚构桥地震反应分析[J].铁道工程学报.2008,10：15-19
[10]蒋成强.桩-土-结构相互作用对铁路大跨连续刚构桥地震反应的影响[J].铁道勘察.2010,5：82-84
[11]李忠献,史志利.行波激励下大跨连续刚构桥的地震反应分析[J].地震工程与工程振动,2003,4
[12]范立础.现代化城市桥梁抗震设计若干问题[J].同济大学学报(自然科学版),1997,(02)
[13]史志利.大跨度桥梁多点激励地震反应分析与MR阻尼器控制[J].天津大学学报,2004
[14]徐艳玲.高墩大跨连续刚构桥弹塑性抗震性能评估[D].陕西：长安大学,2008
[15]李宁.大跨度连续刚构桥地震响应分析[D].四川：西南交通大学,2008
[16]张亚辉等,大跨度连续刚构桥行波效应研究[J].大连理工大学学报,2005,7：480-486
[17]翟东武,高墩大跨桥梁结构非线性地震行为及基于位移的抗震设计方法[D].北京：北方交通大学,2008
[18]谢旭.桥梁结构地震响应分析与抗震设计[M].北京：人民交通出版社,2005
[19]李廉锟.结构力学[M].北京：高等教育出版社,1996
[20]胡聿贤.地震工程学[M].北京：地震出版社,2006
[21]Anil K. Chopra.Dynamics of Structures:Theory and Applications to Earthquake Engineering [M]. Prentice Hall, April 1995
[22]谢礼立,马玉宏.现代抗震设计理论的发展过程[J].国际地震动态.2003,10：1-7
[23]IAEE.Earthquake Resistant Regulations A World List, 1996
[24]汪大绥,贺军利,张凤新.静力弹塑性分析(Pushover Analysis)的基本原理和计算实例[J].世界地震工程.2004(01)
[25]朱玉华,黄海荣,胥玉祥.基于性能的抗震设计研究综述[J].结构工程师.2009(05)
[26]Anil k Chopra,Rakesh k Goel.A modal pushover analysis procedure forestimating seismic demands for buildings. Earthquake Engineering and StructuralDynamics.2002
[27]Applied Technology Council(ATC).Seismic evaluation and retrofit of concrete buildings. Report No.ATC-40.1996
[28]罗文斌,钱稼茹.钢筋混凝土框架基于位移的抗震设计[J].土木工程学报.2003(05)
[29]柳春光,秦泗凤,林皋,等.改进的适应谱Pushover方法评价桥梁结构的抗震性能[J].哈尔滨工业大学学报,2008,40
[30]唐必刚.基于Pushover和能力谱法的桥梁结构抗震性能研究[D].湖南：湖南大学,2010
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